Comparison of endogenous and exogenous RNA primers of poly(U) polymerase in rat hepatic ribosomes

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Abstract
The present work indicates that RNA primer requirements for poly(U) polymerase in the free ribosomes of the rat liver depend upon the degree of enzyme purification. The poly(U) polymerase activity obtained from a crude free ribosomal preparation was compared with the enzymic activity of a partially purified enzyme. After preliminary purification, the enzyme was fractionated by chromatography on Sephadex G-150 and CM-cellulose. Our results demonstrate the presence of several forms of poly(U) polymerase activities, some requiring exogenous RNA and others possessing their own endogenous primer RNA.